KIEV, Ukraine – The rhetorical contest over Ukraine’s Crimean peninsula escalated Friday with Russian lawmakers pledging to welcome the region into Moscow’s fold after a planned referendum on secession and the government in Kiev declaring any such vote illegitimate.

“No one in the civilized world” will recognize the validity of the referendum initiated by pro-Russian representatives in Crimea’s regional assembly and scheduled March 16, warned Ukraine’s interim Prime Minister Arseny Yatsenyuk. He harshly repudiated those agitating for Crimea to break away from Ukraine and join Russia as “separatists and other traitors.”

The plebiscite has been dismissed by Western nations as illegal, a political charade backed by the guns of Russian troops that have surrounded Ukrainian military bases on the strategically important peninsula for days.

But the proposed change in status for Crimea has been rapturously welcomed in Moscow. As thousands of people flooded Red Square to chant support of President Vladimir Putin and of annexing Crimea, members of the Russian parliament promised to expedite the region’s accession to Russia after the vote.

Valentina Matviyenko, the speaker of Russia’s upper chamber and a Putin ally, said Crimea would “become an absolutely equal subject of the Russian Federation” following a thumbs-up in the referendum, the Associated Press reported.

“No one has yet canceled a right to self-determination,” Matviyenko said in televised remarks, dismissing those who oppose the plebiscite.

Crimea has become the main political battlefield between Moscow and Kiev since Ukrainian President Viktor Yanukovich fled Kiev in February after months of street protests. Russia refuses to recognize the new government in Kiev, which wants closer ties with the West instead of with Moscow.

A majority of residents in Crimea are ethnic Russians or Russian speakers. Moscow has described its military incursion there as a mission to protect them, and pro-government media outlets in Russia have painted a grim picture of Crimean Russians being persecuted and fleeing for their lives since the shift of power in Kiev.

But that portrayal has not been substantiated by independent monitors. On Friday, observers from the Organization for Security and Cooperation in Europe were denied entry into Crimea for the second straight day by forces loyal to Russia.

Although Putin denies that Russian troops are involved in the dispute over Crimea, the gunmen he calls members of “local self-defense forces” wear unmarked Russian military uniforms and use Russian military equipment. The peninsula is home to Russia’s Black Sea Fleet.

Tension on the peninsula remains high. Ukraine's Ministry of Defense said Friday that a Russian military truck crashed through the gates of a Ukrainian military base in the port city of Sevastopol and laid siege to the installation, causing dozens of Ukrainian soldiers to hole themselves up in a barracks.

Russian pressure on Kiev on Friday came from another source as well: Gazprom, the private energy company with deep ties to the Russian state, reportedly warned that it may cut off gas exports if the financially strapped Ukrainian government does not pay nearly $2 billion it owes.

Gazprom carried out a similar threat briefly five years ago, which left many Ukrainians shivering in the winter chill and affected supplies destined for other European countries.

Diplomatic efforts to resolve the crisis remained stuck, despite an hourlong telephone call between Putin and President Obama on Thursday.

Washington has slapped some financial and travel sanctions on Russia; the European Union has threatened to do the same if talks between Moscow and Kiev do not begin soon or if the situation deteriorates further.

Russian officials have warned that any economic penalties levied by the West would be met by the same from Moscow.

Michael McFaul, who recently left his post as U.S. ambassador to Russia, said that while U.S. sanctions could hurt Russian businesses, particularly if they include banking penalties, they aren’t likely to dissuade Putin from annexing Crimea.

“At the end of the day, Putin will be willing to make the economic sacrifice if he wants to go ahead with the annexation strategy,” McFaul said.

In Moscow, at the rally in Red Square, demonstrators waved placards proclaiming their loyalty to Putin and declaring that “Crimea is Russian soil.”

Estimates of the number of people attending the rally varied widely between 5,000 and 65,000. State and municipal enterprises gave employees the day off to take part.

Vladimir Konstantinov, the speaker of the Crimean parliament, told the crowds that Crimeans had faith Russia would not abandon them.

“We lost the battle of Kiev,” Konstantinov said. “We understood that we must make a stand in Crimea to the last. We always knew that Russia would never leave us in the lurch and that the Russian people would always be with us.”

Ukraine's worst unrest since the 1991 collapse of the Soviet Union was sparked by ousted President Viktor Yanukovich's decision to scrap a deal with the European Union in favor of closer ties with Russia.

Russian President Vladimir Putin said Wednesday that he had pulled back troops from the border with Ukraine and called on Kremlin-allied separatists to delay a referendum on whether Ukraine's regions should have a greater degree of autonomy.

At least 14 people were killed and scores were wounded as government forces seeking to win back this eastern Ukrainian city from pro-Russia separatists ran into an ambush Monday set up by the rebel gunmen.

A crowd of more than 2,000 pro-Russia separatists on Sunday night seized one of the last key official sites in the eastern Ukraine city of Donetsk still in the hands of the country’s interim government.

Armed clashes left scores of people dead in Ukraine on Friday, as President Obama and German Chancellor Angela Merkel vowed to impose stiffer economic sanctions on Russia if it disrupts Ukraine's upcoming election.